How to easily install Flatpak apps on Elementary OS with Sideload

Sideload is an excellent little utility, that, when installed, makes it incredibly simple to install Flatpak apps on Elementary OS. Follow along with this tutorial as we go over how to set up the tool for your system.

Note: using Sideload requires the absolute latest version of Elementary OS (version 5.0 Juno). Please, before attempting to follow the tutorial, follow these instructions to learn how to upgrade Elementary 4.0 to 5.0.

Enable Flatpak support on Elementary OS

To be able to use the Sideload tool on your Elementary OS PC, you must have the Flatpak protocol set up on your system. To set it up, open up a terminal window by pressing Ctrl + Alt + T or Ctrl + Shift + T,  and install the flatpak package.

sudo apt install flatpak

The above command should be enough to get the Flatpak runtime working on your Elementary OS PC. However, if you’re having issues, please check out our guide on how to enable Flatpak. Be sure also to read the Flatpak website for more information.

Install Sideload on Elementary OS

Sideload has been under development for Elementary OS for 6 months or so. However, it’s not available in AppCenter yet. As a result, the only way to gain access to Sideload is to download the source code, compile it, and install it.

Note: though Sideload is targeted at Elementary OS, it is possible to install on other Linux operating systems, so long as the dependencies are met. For more information on what dependencies are needed, click this page here.

To start the installation of Sideload on Elementary OS, you must first get all of the dependencies installed. Open up a terminal window by pressing Ctrl + Alt + T or Ctrl + Shift + T on the keyboard. Then, from there, use Apt command to load up the dependencies.

sudo apt install git libflatpak-dev libgranite-dev libgtk-3-dev libxml2-dev meson valac

After installing all of the necessary dependencies for Sideload on your Elementary OS PC, run an update and install the latest patches. The latest updates will help the software compilation run smoother.

sudo apt update sudo apt upgrade -y

Following the update process, use the git clone command to download the source code for Sideload on your Elementary OS PC.

git clone https://github.com/elementary/sideload.git

Once the code is done downloading, move the terminal window into the “sideload” folder by using the CD command below.

cd sideload

Inside of the “sideload” directory, use the meson build command to set up the software compilation environment.

meson build --prefix=/usr

When the meson build command is done setting up the build environment, move into it with the CD command below.

cd build

In the Sideload build environment, run the ninja command to compile the source code. Please keep in mind that depending on the hardware specifications of your Elementary OS PC, the compilation process may take a bit of time. Be patient!

ninja

Following the ninja command, the software is compiled and ready to go. At this point, the software must be installed into the root file system of your Elementary OS system. To do that, use the ninja install command below.

sudo ninja install

You can test that Sideload is working by executing io.elementary.sideload in the terminal, but beware, running it from the command-line doesn’t bring up the GUI interface!

io.elementary.sideload

Using Sideload to install Flatpak apps on Elementary OS

The Sideload application works with Flatpak REF files downloaded from the Flatpak Flathub store. To install any Flatpak application on your Elementary OS PC, follow the step-by-step instructions below.

Step 1: Head over to the Flathub website by clicking this link.

Step 2: On the Flathub homepage, click on the search button at the top-right portion of the page. From there, click on the text-box, and type in the name of the program you’d like to install. In this example, we will use Skype.

Step 3: Select the app you want to install in the search results to go to its page on the Flathub website.

Step 4: After making your way to the app’s Flathub page, locate the “install” button, and click on it with the mouse. Selecting the “Install” button will download the Flatpak REF file to your computer in the “Downloads” folder

Step 5: Click on the “Applications” button and search for “Files.” Then, launch the “Files” app on the Elementary OS desktop.

Step 6: Inside of the “Files” app, locate the “Downloads” folder and select it with the mouse to access the downloaded Flatpak REF file.

Step 7: Inside of the “Downloads” folder, double-click on the Flatpak REF file. Or, right-click on it and select “Sideload” to open it.

Step 8: With the Flatpak REF file open in Sideload, a message will appear. This message will ask if you’d like to “install untrusted” app. Check the “I understand” button and select “Install Anyway.”

Step 9: Allow your Flatpak app to install from the Flathub store.

When your app is done installing with Sideload, you will be able to access it in the “Applications” menu.